According to a publication by J.M. Hall, the "discovery well in 1922 at Cambridge was at a depth of 3,470 feet, which was 1245 feet below the top of the "Big Lime," and gas was encountered with an open flow of 8,000 M, and a rock pressure of 1,150 pounds. By 1925 eleven wells had been completed in this area and the field had started to go to water." Since the 1950s Columbia Gas Transmission Corporation converted 48 of the wells to gas storage1 . The EIA lists Guernsey Storage as having a capacity of 7.3 BCF and a maximum daily deliverability of 36.6 MMSCF2 .

Around the Appalachian Basin the Oriskany sandstone is known as one of the toughest sands to drill and fracture stimulate. Perhaps, the most extreme example lies under the NW corner of Guernsey County, Ohio (Figure 1). One interesting geological point of interest here is that the Cambridge cross-strike structural discontinuity is located on the western edge of the gas storage field in Guernsey County. The Appalachian Gas Atlas states that there is "no reflection or influence of this basement activity on the Devonian Oriskany."

Figure 1

Arrow points to approximate location of Columbia Gas Transmission Corp's Guernsey Oriskany storage field.

Figure 1

Arrow points to approximate location of Columbia Gas Transmission Corp's Guernsey Oriskany storage field.

Columbia Gas Transmission Corp, as part of its well reconditioning program, routinely works over some of the wells in this field. Hydraulic fracturing is part of the work-over process to restore lost deliverability. This paper will explore the high surface pressure responses seen during both original frac jobs and refracturing treatments. The fracturing gradients are routinely in excess of the overburden gradient. Interestingly, these same pressures are not experienced in the Silurian age Clinton sandstone that lies below the Oriskany across the field. The treating pressures prompted further investigation to determine their origin and to help improve future stimulation treatment designs. Three- (3) additional wells were to be stimulated this spring in the Guernsey field and their pressure response will be included in this paper.

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